RESUMEN

Freeze casting has emerged as one of the most promising manufacturing methods to fabricate porous scaffolds in recent years. This is due to various reasons which include a wide range of materials which can be used in this process, easiness of the process, etc. One of the major objectives of this work was to fabricate bone-like structure by using a modified freeze casting process. In this work, Hydroxyapatite and Tricalcium phosphate scaffolds with bone-like structure were fabricated by understanding and utilizing the basic physics of freeze casting. Thermal conductivity of the base plate is a crucial factor for obtaining controlled pore and porosity distribution in a porous scaffold. It was found that designing the base plate with variable thermal conductivity has led to the formation of bone-like structure. Porous scaffolds were quantitatively analyzed for pore size and porosity distribution at center and circumference. Porosity at circumference was observed to be approximately dropped by 55%, a similar trend was seen for pore size. Therefore, it was significant evidence that modified freeze casting has capable in fabricating bone-like structures with ease and good control. This will open many new applications of porous scaffolds in biomedical, energy devices, chemical catalyst and many more.

RESUMEN

The long standing need of the implant manufacturing industries is to fabricate multi-matrix, customized porous scaffold as cost-effectively. In recent years, freeze casting has shown greater opportunity in the fabrication of porous scaffolds (tricalcium phosphate, hydroxyapatite, bioglass, alumina, etc.) such as at ease and good control over pore size, porosity, a range of materials and economic feasibility. In particular, tricalcium phosphate (TCP) has proved as it possesses good biocompatible (osteoinduction, osteoconduction, etc.) and biodegradability hence beta-tricalcium phosphate (ß-TCP, particle size of 10µm) was used as base material and camphene was used as a freezing vehicle in this study. Both freezing conditions such as constant freezing temperature (CFT) and constant freezing rate (CFR) were used for six different conditional samples (CFT: 30, 35 and 40vol% solid loading; similarly CFR: 30, 35 and 40vol% solid loading) to study and understand the effect of various properties (pore size, porosity and compressive strength) of the freeze-cast porous scaffold. It was observed that the average size of the pore was varying linearly as from lower to higher when the solid loading was varying higher to lower. With the help of scanning electron micrographs (SEM), it was observed that the average size of pore during CFR (9.7/ 6.5/ 4.9µm) was comparatively higher than the process of CFT (6.0/ 4.8/ 2.6µm) with respect to the same solid loading (30/ 35/ 40vol%) conditions. From the Gas pycnometer analysis, it was found that the porosity in both freezing conditions (CFT, CFR) were almost near values such as 32.8% and 28.5%. Further to be observed that with the increase in solid loading, the total porosity value has decreased due to the reduction in the concentration of the freezing vehicle. Hence, the freezing vehicle was found as responsible for the formation of appropriate size and orientation of pores during freeze casting. The compressive strength (CS) testing was clearly indicated that the CS was majorly depending on the size of pore which was depending on solid loading. The CS of CFT-based samples (smaller pore sizes and higher resistance to the propagation of crack) were higher due to the higher solid content (pore size) in compared with CFR-based samples on the similar solid loading conditions. As evidently, it was noted that the CFT-based sample with 40% solid loading has given the compressive strength which has come in the range of cancellous bone. The positive note was that the ratio of Ca/P has come as 1.68 (natural bone) after sintering and that was the required value recommended by the food and drug administration (FDI) for manufacturing of bone implants.

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OBJECTIVE: To assess the efficacy of 9-month short-course chemotherapy (SCC) and to study the pattern of neurological recovery in patients with Pott's paraplegia. DESIGN: Patients with recent onset of spastic paraplegia due to clinically and radiologically active spinal tuberculosis involving vertebral bodies of level D4-L1 were treated with streptomycin, rifampicin, isoniazid and ethambutol daily for the first 2 months, followed by rifampicin plus isoniazid twice weekly for the next 7 months. The study was conducted in 2 phases. In the first phase 10 patients were admitted to the open trial where all patients had undergone modified Hong Kong surgery in addition to chemotherapy. In the next phase 23 patients enrolled in the study were randomly allocated to receive either chemotherapy alone or surgery plus chemotherapy. All the patients were followed for 5 years from the start of treatment. A scoring system was devised to predict neurological recovery. RESULTS: In all, 33 patients were admitted and treated with SCC. Thirteen patients were allocated to the chemotherapy (CHEM) regimen; of these 3 patients had to be operated upon for clinical deterioration; the remaining 20 had surgery plus chemotherapy; 4 were excluded for various reasons, leaving 29 patients in the analysis. None relapsed requiring treatment. CONCLUSION: A combination of surgery (when indicated) and SCC of 9 months' duration is effective in the treatment of Pott's paraplegia. All patients had neurological recovery by the end of 9 months; 8 recovered with chemotherapy alone. Complete motor recovery was seen in 62% by the 3rd month and 90% by the 6th month.

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The case of eighty-one patients who had tuberculosis of the spine that was treated by debridement and anterior arthrodesis were reviewed eight years or more postoperatively. We studied the progression of the kyphosis and evaluated the function and fate of the bone grafts that were used. At eight years, the results with respect to the progression of the kyphosis were classified as excellent or good in forty-eight patients (59 per cent), all of whom had had minimum destruction of the vertebral bodies; limited surgical excision of bone, resulting in a small post-debridement defect that needed only a short graft; marked intraoperative correction of the deformity; and involvement of lower lumbar segments. Fifteen patients (19 per cent) had a fair result and eighteen (22 per cent), a poor result. An increase in the deformity was common in patients who had extensive involvement of the vertebral bodies that had resulted in a large post-debridement defect necessitating a graft spanning more than two disc spaces. Lesions of the thoracic vertebrae were associated with many of the poor results, and patients who had a marked kyphosis before treatment also did not do well. A stable graft that provided structural support was observed in only thirty-three patients (41 per cent), and failure of the graft due to slippage, fracture, absorption, or subsidence was seen in forty-eight patients (59 per cent). The length of the graft also played a role: the graft failed most often in patients in whom it spanned more than two disc spaces. We concluded that it is unwise to rely solely on the graft to prevent vertebral collapse in patients in whom the length of the graft exceeds two disc spaces. These patients may benefit from additional measures, such as an extended period of non-weight-bearing, posterior arthrodesis after six to twelve weeks, and prolonged use of a brace until complete consolidation is evident.

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